Illustration copyright 2004 by Nucleus Communications, Inc. All rights reserved. http://www.nucleusinc.com

Normally, the placenta is attached to the uterus above the cervix. When the placenta is blocking the cervix, it is called placenta previa. The amount of cervix covered by the placenta may be slight (marginal), moderate (partial), or complete (total). This illustration shows a complete placenta previa.